Electron-Cyclotron Current Drive at the Second Harmonic in the WT-3 Tokamak

Electron cyclotron current drive (ECCD) at the second harmonic (ω=2Ω_e) is demonstrated for two types of plasma in the WT-3 tokamak. When microwave power P_EC is injected into a plasma after Ohmic heating (OH) power is shut down, the plasma current is sustained and ramped up by the EC wave only. Here 2Ω_e EC-driven current is generated by 2Ω_e EC heating of an energetic electron tail existing in the OH plasma. Further, when P_EC is injected into a microwave discharge plasma, 2Ω_e EC-driven plasma current is started up and 2Ω_3 ECCD plasma is formed without OH power. The 2Ω_e ECCD efficiency is the same order as that at ω=Ω_e, but the 3Ω_e EC-driven current is not generated, in contrast with the theoretical prediction